A typical alternating-current surface discharge type panel used as a plasma display panel (hereinafter referred to as “panel”) has many discharge cells between a front plate and a back plate that are faced to each other.
In the front plate, a plurality of display electrode pairs each of which is formed of a scan electrode and a sustain electrode are disposed in parallel on a front glass substrate. In the back plate, a plurality of data electrodes are disposed in parallel on a back glass substrate. The front plate and back plate are faced to each other so that the display electrode pairs and the data electrodes intersect three-dimensionally, and are sealed. Discharge gas is filled into a discharge space in the sealed product. Discharge cells are disposed in intersecting parts of the display electrode pairs and the data electrodes.
A subfield method is generally used as a method of driving the panel. In this method, one field period is divided into a plurality of subfields, and the subfields at which light is emitted are combined, thereby performing gradation display. Each subfield has an initializing period, an address period, and a sustain period. In the initializing period, initializing discharge occurs, and a wall charge required for a subsequent address operation is formed on each electrode. In the address period, scan pulses are sequentially applied to scan electrodes, an address pulse is selectively applied to a data electrode of a discharge cell where display is to be performed to cause address discharge. In the sustain period, a sustain pulse is alternately applied to the display electrode pairs, sustain discharge is caused in the discharge cell where address discharge has been performed, and light is emitted, thereby displaying an image.
In such a plasma display device, the drawing section of each electrode is electrically connected to the output section of each driving circuit via a flexible flat cable (hereinafter referred to as “FFC”), and driving voltage is applied to each electrode via the FFC to drive the panel. For example, the output section of each driving circuit has a connector for being connected to the FFC. One end of the FFC whose the other end is fixed to the drawing section of the panel is connected to the connector, thereby electrically connecting each electrode to each driving circuit.
At this time, when there is an FFC that is not connected appropriately, the panel cannot be driven normally. A technology is proposed where a connection failure can be detected with color change of paint by arranging resistors electrically in series (patent document 1, for example). Here, each of the resistors is formed by coating each circuit pattern of the FFC with temperature indicating paint.
When one electric circuit is divided and mounted on a plurality of printed boards, and difference (hereinafter referred to as “potential shift”) occurs between reference potentials such as ground potentials, noise can be caused by the potential shift in a signal delivered between the printed boards and malfunction can be caused. Therefore, when one electric circuit is divided and mounted on a plurality of printed boards, it is important that the reference potentials between the printed boards are previously set to be equal.
For setting the reference potentials (hereinafter, it is assumed that the ground potential is reference potential) between the printed boards to be equal, generally, the ground potentials of the printed boards are electrically interconnected using a wire. At this time, for minimizing the impedance between the ground potentials of the printed boards, generally, the impedance of the wire for interconnecting the ground potentials is reduced, and one printed board has two or more parts for interconnecting the ground potential of the one printed board to that of the other printed board.
The size of the panel has been recently increased. While, the size of a printed board having a driving circuit is restricted due to various factors. Therefore, in a plasma display device employing an enlarged panel that is difficult to be structured so that each electrode is driven only by one printed board, a plurality of printed boards must be used in order to drive each electrode.
In a plasma display device that has such an enlarged panel and has a scan electrode driving circuit dividedly mounted on a plurality of printed boards, the ground potentials of the printed boards are electrically interconnected, one printed board has a plurality of connecting parts between the ground potential of the one printed board and that of the other printed board. Thanks to this structure, the potential shift between the ground potentials of the printed boards is suppressed, and the scan electrode can be driven stably.
When an FFC is used for interconnecting the ground potentials of the printed boards, and all of a plurality of wires disposed inside the FFC are used for interconnecting the ground potentials, the impedance between the ground potentials can be suppressed to be low.
In this structure, however, the ground potentials are interconnected via a plurality of connecting parts. Therefore, even if a connection failure such as an accident that one of the FFCs used for interconnecting the ground potentials departs from the connector occurs, the ground potentials are not always put into an electrically disconnected state. The connection failure of the FFC increases the impedance between the ground potentials, so that a phenomenon that noise increases in the driving waveform applied to the scan electrode occurs, but the scan electrode driving circuit itself operates. It is difficult that a glance at a display image allows a checker to judge whether a connection failure occurs in the FFC for interconnecting the ground potentials.
[Patent document 1] Japanese Patent Unexamined Publication No. H02-186531